Study On Properties Of PI/Nano-Mg?OH?₂ Hybrid Film

Polyimide films for its excellent electrical properties are widely used in fields such as inverter motor.But the space charge effect often results in premature damage of polyimide film on inverter motor.Therefore,the development of polyimide film which can suppress the space charge effect has great significance for the development of inverter motor.In this paper,a series of magnesium hydroxide nano-composite films with different doping quantity were prepared by in-situ polymerization method.Further,the nano-Mg?OH?₂ modified by silane coupling agent KH560 and a series of magnesium hydroxide nano-composite films with different coupling agent content were prepared.Doping quantity of the nano-Mg?OH?₂ set as 1 wt%,2 wt%,4 wt%,8 wt%and the content of coupling agent set as 1 wt%,2 wt%,3 wt%,4 wt%.Properties of unmodified and modified hybrid films including the morphology,IR spectrum,dielectric properties,electrical breakdown field strength and mechanical properties were characterized and tested.The scanning electron microscope results show that nano-Mg?OH?₂ agglomerates in the polyimide and the dispersion of nano-Mg?OH?₂ modified by coupling agent is improved in composites and the size of particles become smaller.The electric current test results show that the electric degradation threshold of composites is more than that of pure polyimide and with the increase of nano-Mg?OH?₂ content.the electric degradation threshold increases,furthermore the electric degradation threshold of composites modified with coupling agent further increases.Based on these results we find that nano-Mg?OH?₂ can restrain space charge accumulation and the more content of nano-Mg?OH?₂,the stronger suppression of space charge accumulation and nano-Mg?OH?₂ can be enhanced by coupling agent to restrain space charge accumulation.The electrical breakdown field strength results show that nano-Mg?OH?₂ makes the breakdown strength of polyimide decreased but the 2 wt%nano-Mg?OH?₂ content composite modified by 1 wt%coupling agent content which breakdown strength reaches to 389 kV/mm has 5.3%higher than that of pure polyimide.However,the insulation resistance and the tensile strength of composites modified or unmodified by coupling agent are all lower than that of pure polyimide.